During processing of the light sensitive material it is necessary to wash the material after a chemical treatment to remove chemical ingredients used in the treatment. Such washing is generally carried out by transporting the light sensitive material through a wash chamber containing water supplied from a domestic water source. Means are generally provided to periodically or continuously replenish the wash water to avoid the build up of contaminants such as salts in the wash water. However, it is desirable to minimize replenishment to reduce water consumption and waste water discharge.
One of the problems in hard or saline water regions is that the fresh water itself contains salts. If an ionic conductivity sensor is used to regulate the amount of water replenishment during the washing process, the presence of such salts can result in a false identification of the residual salts in the water from the washing function. This is because ionic conductivity sensors do not distinguish between different ions well. Thus it is difficult to determine the concentrations of salts in the fresh water relative to that produced by the washing process to accurately control water replenishment to achieve water conservation.